\fIHost\fR in this context means the platform hosting the build process, i.e.
what autotools calls CBUILD.
Its packages are contained in the root of the filesystem ("\fI/\fR").
+
If \fBROOT\fR is "\fI/\fR", all dependency types will be installed there.
Otherwise, for EAPIs that support \fBHDEPEND\fR (experimental
\fBEAPI 5-hdepend\fR), only \fBHDEPEND\fR is installed into "\fI/\fR".
If it is different from "\fI/\fR", i.e. \fIhost\fR and \fItarget\fR are not the
same, this variable contains the path to the directory housing the \fItarget\fR
system.
+
For EAPIs that support \fBHDEPEND\fR (experimental \fBEAPI 5-hdepend\fR),
\fBDEPEND\fR, \fBRDEPEND\fR, and \fBPDEPEND\fR
list the \fItarget\fR dependencies, i.e. those to be installed into \fBROOT\fR.